Head drive device and inkjet recording device

Abstract

To enhance a degree of freedom of control of a dot diameter to one dot in multidrop.SOLUTION: In a head driving device 100 having a driving circuit 110 for applying a driving voltage to a nozzle actuator, and a control part 101 for controlling driving of the driving circuit 110, the driving circuit 110 includes a plurality of boosting units C1 and C2 capable of generating a voltage superposed on a first power source voltage Va, and a plurality of switching parts S1 to S4 for switching a plurality of voltages generated by the plurality of boosting parts C1 and C2. The control part 101 controls operation of the plurality of switching parts S1 to S4, selectively superposes a plurality of voltages generated in the plurality of boosting parts C1 and C2 on the first power source voltage Va, and generates a driving voltage.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a head driving device for driving an inkjet head provided with a nozzle, and an inkjet recording apparatus.

Background Art

[0002] Conventionally, as a means for realizing gradation expression with an inkjet head in an inkjet recording apparatus, a technique of adjusting the amount of droplets per dot by multi-drop is known. Multi-drop is a technique for changing the dot diameter by controlling the number of droplets ejected for one dot of a document image. The larger the number of droplets ejected for one dot, the larger the dot diameter, and the darker the color and density of the dot recorded on the recording material.

[0003] However, in the case of a push-pull drive circuit using a constant voltage source and a switching element, the voltage value of a multi-drop drive voltage waveform (on period) in which there are a plurality of on periods for one dot is always constant.

[0004] For example, Patent Document 1 discloses a head driving device for an inkjet printer including a boosting means for amplifying the voltage of a driving signal generated by a driving waveform generation circuit by a current amplification circuit and further boosting the voltage of the driving signal output from the current amplification circuit. In the head driving device disclosed in Patent Document 1, a desired driving voltage is generated by boosting with a bootstrap circuit even at a low power supply voltage. That is, as a means for generating a target single voltage, a method of boosting the voltage of a driving signal by a bootstrap circuit is used.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] However, in the case of the technology disclosed in Patent Document 1, the voltage of the drive signal can only be boosted by one step. There is only one voltage value for the ON period of the generated drive voltage, and this voltage value is always output as the multidrop drive voltage. In other words, in multidrop, for example, the droplet volume (dot diameter) of each ink droplet, such as the first, second, and third droplets, cannot be varied. Thus, conventionally, the degree of freedom in controlling the dot diameter for a single dot in multidrop has been low.

[0007] Given the above situation, there was a need for a method to increase the degree of freedom in controlling the dot diameter for each individual dot in multidrop imaging. [Means for solving the problem]

[0008] To solve the above problems, a head drive device according to one aspect of the present invention is a head drive device for an inkjet recording device that ejects ink droplets from nozzles, comprising a drive circuit that applies a drive voltage to nozzle actuators provided corresponding to the nozzles of an inkjet head, and a control unit that controls the drive of the drive circuit. The drive circuit comprises a plurality of boost units that can generate a voltage superimposed on a first power supply voltage using a second power supply voltage, and a plurality of switching units that can switch between the plurality of voltages generated by the plurality of boost units. The control unit controls the operation of the plurality of switching units and generates a drive voltage by selectively superimposing the plurality of voltages generated by the plurality of boost units onto the first power supply voltage. Furthermore, an inkjet recording apparatus according to one aspect of the present invention is an inkjet recording apparatus equipped with the head drive device described above. [Effects of the Invention]

[0009] According to at least one aspect of the present invention, by selectively superimposing multiple voltages on a first power supply voltage to generate a drive voltage for a nozzle actuator, the degree of freedom in controlling the dot diameter for a single dot in a multidrop system can be increased. Other issues, configurations, and effects not mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit diagram showing an example of a typical head drive mechanism for an inkjet recording device. [Figure 2] This waveform diagram shows an example of a multidrop drive voltage. [Figure 3] This is a schematic diagram showing an example of the overall configuration of an inkjet recording device according to one embodiment of the present invention. [Figure 4] This is a plan view showing the head unit of an inkjet recording apparatus according to the first embodiment of the present invention, as seen from the recording material side. [Figure 5] This is a block diagram showing an example of the hardware configuration of an inkjet recording apparatus according to the first embodiment of the present invention. [Figure 6] This is a circuit diagram showing an example of a head drive device included in an inkjet recording device according to one embodiment of the present invention. [Figure 7] This figure shows the state when a charge is applied to the boost circuit in a drive circuit according to one embodiment of the present invention, and the equivalent circuit of the drive circuit. [Figure 8] This figure shows the state when the charge charged in the boost circuit is superimposed on the output of the drive circuit in a drive circuit according to one embodiment of the present invention, and the equivalent circuit of the drive circuit. [Figure 9] This waveform diagram shows an example of a multidrop drive voltage related to one embodiment of the present invention. [Modes for carrying out the invention]

[0011] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the accompanying drawings. Components having substantially the same function or configuration in this specification and the accompanying drawings are denoted by the same reference numerals, and redundant descriptions are omitted.

[0012] [Typical drive circuit] First, the head driving device included in a conventional general inkjet recording apparatus will be described with reference to FIG. 1. FIG. 1 is a circuit diagram showing an example of a general head driving device of an inkjet recording apparatus.

[0013] The head driving device 200 shown in FIG. 1 includes a control circuit 201, a drive signal generation circuit 202, and a drive circuit 210. The drive signal generation circuit 202 generates a drive signal to be supplied to the series-connected switching elements 203 and 204 formed in the drive circuit 210 based on a control signal output from the control circuit 201. The switching elements 203 and 204 turn on or off according to the drive signal, and charge the power supply voltage Va output from the power supply circuit 205 (constant voltage source) to the capacitive load 206 or discharge the power supply voltage Va charged in the load 206. The load 206 is a piezoelectric element (piezo element) of a nozzle actuator provided for each nozzle of the inkjet head. Thus, the power supply voltage Va is applied as the drive voltage of the load 206.

[0014] FIG. 2 is a waveform diagram showing an example of a multi-drop drive voltage. In the case of the head driving device 200 shown in FIG. 1, as the multi-drop drive voltage waveform, no matter how many shots are made, the voltage during the on period (high level side) is always the same voltage, that is, only the power supply voltage Va output from the power supply circuit 205. Therefore, as shown in FIG. 2, for example, the dot diameters of the ink droplets D1 to D3 ejected continuously three times for one dot are all the same.

[0015] Therefore, in the present invention, a plurality of voltages are generated by a booster circuit, and the plurality of voltages are selectively switched and superimposed on the power supply voltage Va, so that the value of the drive voltage can be switched for each ejection of an ink droplet during multi-drop.

[0016] [Overall Configuration of Inkjet Recording Apparatus] First, a configuration example of an inkjet recording apparatus according to an embodiment of the present invention will be described with reference to FIG. 1. FIG. 3 is a schematic diagram showing an example of the overall configuration of an inkjet recording apparatus according to an embodiment.

[0017] The inkjet recording apparatus 1 forms (records) an image on a recording material P (recording medium) by ejecting ink from nozzles 244 provided in an inkjet head 242 shown in FIG. 4 described later. In the present embodiment, an example in which paper is applied as the recording medium will be described, but the present invention is not limited to this, and various other materials such as films and fabrics can be applied as the recording medium.

[0018] This inkjet recording apparatus 1 is a color inkjet recording apparatus that superimposes four colors of ink: yellow (Y), magenta (M), cyan (C), and black (Bk). The inkjet recording apparatus 1 includes a paper feeding unit 10, an image forming unit 20, a paper discharging unit 30, and a control unit 40. Then, the inkjet recording apparatus 1 forms the image data input from the terminal device 2 (see FIG. 5) on the recording material P.

[0019] The paper feeding unit 10 includes a paper feeding tray 11 and a recording material supply unit 12. The paper feeding tray 11 is a plate-like member provided so that the recording material P can be placed thereon. The paper feeding tray 11 is provided so as to be movable in the vertical direction according to the number of sheets of the recording material P placed thereon. Then, the uppermost recording material P in the vertical direction among the plurality of recording materials P placed on the paper feeding tray 11 is held at a position where it is conveyed by the recording material supply unit 12.

[0020] The recording material supply unit 12 includes a plurality (two in this example) of rollers 121 and 122 and a conveyance belt 123. The conveyance belt 123 is formed in an endless shape with both ends in the longitudinal direction connected. The conveyance belt 123 is stretched over the rollers 121 and 122. Then, when one of the rollers 121 and 122 is rotationally driven, the conveyance belt 123 circulates between the two rollers 121 and 122. As a result, the recording material P placed on the conveyance belt 123 is conveyed.

[0021] Furthermore, the recording material supply unit 12 includes a drive unit (not shown) that rotates the rollers 121 and 122, and a supply device (not shown) that transfers the uppermost recording material P placed on the paper tray 11 to the transport belt 123. The recording material supply unit 12 then transports the recording material P placed on the transport belt 123 toward the image forming unit 20 and feeds it to the image forming unit 20.

[0022] The image forming unit 20 includes an image forming drum 21, a transfer unit 22, a heating unit 23, a head unit 24, a fixing unit 25, an image reading unit 26, a recording material ejection unit 27, and a recording material inversion unit 28, and forms an image on the recording material P.

[0023] The image forming drum 21 is cylindrical in shape. The image forming drum 21 rotates counterclockwise by a drive motor (not shown). Recording material P supplied from the paper feeding unit 10 is carried on the outer circumferential surface of the image forming drum 21. The image forming drum 21 has three holding regions 211, which are three equal parts of the outer circumferential surface. The holding regions 211 have a resin sheet or the like attached to the surface of a stainless steel (SUS) sheet or the like, making it possible to hold the recording material P on the surface of each holding region 211. The image forming drum 21 is rotated to transport the recording material P toward the paper discharge unit 30. A heating unit 23, a head unit 24, a fixing unit 25, and an image reading unit 26 are arranged opposite each other on the outer circumferential surface of the image forming drum 21.

[0024] The transfer unit 22 is provided between the recording material supply unit 12 and the image forming drum 21 of the paper feeding unit 10. The transfer unit 22 has a claw portion 221 and a cylindrical transfer drum 222, etc. The claw portion 221 holds one end of the recording material P conveyed by the recording material supply unit 12. The transfer drum 222 guides the recording material P held by the claw portion 221 toward the image forming drum 21. As a result, the recording material P is transferred from the recording material supply unit 12 to the outer surface of the image forming drum 21 via the transfer unit 22.

[0025] A heating unit 23 is located downstream of the transfer drum 222 in the direction of transport of the recording material P. The heating unit 23 has, for example, an electric heating element and generates heat in response to the application of electricity. The heating unit 23 generates heat under the control of the control unit 40 so that the recording material P, which is carried on the image forming drum 21 and passes near the heating unit 23, reaches a predetermined temperature.

[0026] Furthermore, a temperature sensor (not shown) is provided near the heating unit 23. The temperature sensor detects the temperature near the heating unit 23. The control unit 40 then controls the temperature of the heating unit 23 based on the temperature information detected by the temperature sensor.

[0027] A head unit 24 is provided on the downstream side of the heating section 23 in the direction of transport of the recording material P. There are four head units 24, corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk). The four head units 24 are arranged in the order of yellow, magenta, cyan, and black from the upstream side in the direction of transport of the recording material P.

[0028] The head unit 24 is set to a length (width) that covers the entire recording material P in a direction perpendicular to the transport direction of the recording material P (width direction). In other words, the inkjet recording device 1 is a one-pass line head type inkjet recording device. The four head units 24 have the same configuration as each other, except that they eject different colored inks.

[0029] Next, an example configuration of the head unit 24 of the inkjet recording device 1 will be described. Figure 4 is a plan view showing the head unit 24 as seen from the recording material side.

[0030] The head unit 24 (an example of a head drive device) has multiple (16 in this example) inkjet heads 242 (an example of an ink ejection unit). Two inkjet heads 242 form one pair to constitute one inkjet module 243. Therefore, the head unit 24 in this example is equipped with eight inkjet modules 243.

[0031] The eight inkjet modules 243 are arranged in two rows along the transport direction of the recording material P. Each row of inkjet modules 243 is arranged in a row of four along a direction perpendicular to the transport direction of the recording material P (the width direction). Furthermore, the eight inkjet modules 243 are arranged in a staggered pattern, alternating between the two rows of inkjet modules 243 along the transport direction of the recording material P.

[0032] The number and arrangement of the inkjet modules 243 are not limited to those described above, and six or more inkjet modules 243 may be arranged.

[0033] Furthermore, the inkjet head 242 has multiple nozzles 244. The inkjet head 242 ejects ink from the nozzles 244 toward the recording material P. As a result, an image is formed on the recording material P supported on the image forming drum 21.

[0034] A fixing unit 25 is located downstream of the four head units 24 in the transport direction. For example, a fluorescent tube that emits ultraviolet light, such as a low-pressure mercury lamp, is used as the fixing unit 25. The fixing unit 25 irradiates ultraviolet light toward the recording material P transported by the image forming drum 21, curing the ink ejected onto the recording material P. In this way, the fixing unit 25 fixes the image formed on the recording material P.

[0035] Examples of fluorescent tubes that emit ultraviolet light include low-pressure mercury lamps, mercury lamps with operating pressures of several hundred Pa to 1 MPa, light sources that can be used as germicidal lamps, cold cathode tubes, ultraviolet laser light sources, metal halide lamps, and light-emitting diodes. Among these, light sources that can irradiate ultraviolet light at a higher intensity and consume less power (such as light-emitting diodes) are more desirable.

[0036] Furthermore, the fixing unit 25 is not limited to one that irradiates with ultraviolet light; any unit that irradiates with energy rays having the property of curing the ink according to the properties of the ink is acceptable, and the light source can also be replaced according to the wavelength of the energy rays. Also, the fixing unit 25 is not limited to one that irradiates with light such as ultraviolet light. As a fixing unit, various methods can be applied, such as drying the ink by applying heat to the recording material, or applying a liquid that causes a chemical change to the ink.

[0037] Furthermore, an image reading unit 26 is located downstream of the fixing unit 25 in the transport direction. The image reading unit 26 irradiates the object to be read from a light source and reads the reflected image. The image reading unit 26 is composed of an inline sensor in which multiple detection elements are arranged along a direction perpendicular to the transport direction of the recording material P (width direction), and reads the two-dimensional reflected image formed on the recording material P by the head unit 24 and the fixing unit 25, as well as the reflected image of the surface of the image forming drum 21. The image data read by the image reading unit 26 is sent to the control unit 40.

[0038] Furthermore, the spacing between the detection elements constituting the image reading unit 26 is set wider than the spacing between the nozzles 244 of the inkjet head 242. In other words, the resolution of the image reading unit 26 is set to be coarser than the resolution of the head unit 24. In addition, the image reading unit 26 is formed to be longer than the width of the image forming drum 21, so that it can read the entire width of the holding area 211 on the surface of the image forming drum 21.

[0039] Furthermore, a recording material discharge unit 27 and a recording material inversion unit 28 are provided downstream of the image reading unit 26 in the transport direction. The recording material discharge unit 27 transports the recording material P transported by the image forming drum 21 toward the paper discharge unit 30.

[0040] The recording material discharge unit 27 includes a cylindrical separation drum 271 and a discharge belt 272. The separation drum 271 separates the recording material P supported on the image forming drum 21 from the outer surface of the image forming drum 21. The separation drum 271 then guides the recording material P to the discharge belt 272 or the recording material reversal unit 28.

[0041] The separation drum 271 guides the recording material P to the discharge belt 272 when performing face-up paper discharge in single-sided image formation. The separation drum 271 also guides the recording material P to the recording material inversion unit 28 when performing face-down paper discharge in single-sided image formation or double-sided image formation.

[0042] The discharge belt 272 is formed in an endless shape, similar to the conveyor belt 123 of the recording material supply unit 12. The discharge belt 272 is rotatably supported by a plurality of rollers. The discharge belt 272 sends the recording material P received by the separation drum 271 to the paper discharge unit 30.

[0043] The recording material inversion unit 28 has a plurality of inversion rollers 281, 282 and an inversion belt 283. When performing face-down paper discharge, the recording material inversion unit 28 inverts the front and back sides of the recording material P guided by the separation drum 271 and transports it to the recording material discharge unit 27. As a result, the recording material P is transported to the paper discharge unit 30 with the side on which the image formed by the recording material discharge unit 27 faces downward in the vertical direction.

[0044] Furthermore, when performing double-sided image formation, the recording material inversion unit 28 inverts the front and back sides of the recording material P guided by the separation drum 271 and transports it again to the outer surface of the image forming drum 21. As a result, the recording material P is transported by the image forming drum 21 and passes again through the heating unit 23, head unit 24, fixing unit 25, and image reading unit 26.

[0045] The paper discharge unit 30 stores the recording material P that has been sent out from the image forming unit 20 by the recording material discharge unit 27. The paper discharge unit 30 has a flat paper discharge tray 31. The paper discharge unit 30 then places the recording material P on which an image has been formed on the paper discharge tray 31.

[0046] [Hardware configuration of inkjet recording devices] Next, we will describe an example of the hardware configuration of the inkjet recording device 1. Figure 5 is a block diagram showing an example of the hardware configuration of the inkjet recording device 1.

[0047] The inkjet recording device 1 includes a control unit 40. The control unit 40 includes, for example, a CPU (Central Processing Unit) 41, a RAM (Random Access Memory) 42 used as a workspace for the CPU 41, and a ROM (Read Only Memory) 43 for storing programs executed by the CPU 41. Furthermore, the control unit 40 has a storage unit 44 consisting of a hard disk drive (HDD) or semiconductor memory as a large-capacity storage device. The storage unit 44 stores information for controlling the inkjet recording device 1, such as control programs (for example, image processing programs) and various data. Therefore, the ROM 43 and the storage unit 44 record programs and data necessary for the operation of the CPU 41. In other words, the ROM 43 and the storage unit 44 are used as an example of a computer-readable recording medium that stores programs executed by a computer that operates the inkjet recording device 1.

[0048] Furthermore, the inkjet recording device 1 includes a transport unit 51 that drives the transport system, such as the image forming drum 21, the recording material ejection unit 27 and the recording material inversion unit 28, to transport the recording material P, an operation display unit 52 and an input / output interface 53.

[0049] The CPU 41 of the control unit 40 is connected to the heating unit 23, head unit 24, fixing unit 25, image reading unit 26, RAM 42, ROM 43, and storage unit 44 via the system bus 54, and controls the entire device. The CPU 41 is also connected to the transport unit 51, operation display unit 52, and input / output interface 53 via the system bus 54.

[0050] The operation display unit 52 is a touch panel consisting of a display such as a liquid crystal display (LCD) or an organic ELD (Electro-Luminescence Display). This operation display unit 52 displays information related to the inkjet recording device 1, such as instruction menus for the operator, information related to the nozzle 244 ejection detection operation, and information related to acquired image data. Furthermore, the operation display unit 52 is equipped with multiple keys and acts as an input unit that accepts input of various instructions, characters, numbers, and other data from the operator through key operations. This allows the operator to operate the inkjet recording device 1 through the operation display unit 52. The operation display unit 52 may also be configured as an operation unit and a display unit. In this case, the operator operates the inkjet recording device 1 through the operation unit, and the display unit displays information related to the inkjet recording device 1.

[0051] The input / output interface 53 is connected to a terminal device 2, such as a PC (personal computer) or a facsimile machine. The input / output interface 53 receives image data from the terminal device 2. The input / output interface 53 outputs the received image data to the control unit 40. The control unit 40 then performs image processing on the image data received from the input / output interface 53, such as shading correction, image density adjustment, and image compression, as needed.

[0052] Furthermore, the head unit 24 receives image data processed by the control unit 40 and forms a predetermined image on the recording material P based on the image data. Specifically, the head unit 24 drives the head drive unit 241 to eject ink from the inkjet head 242 to a predetermined position. The head drive unit 241 is equipped with multiple drive circuits 110 that apply a drive voltage to a load 112 (piezoelectric element) provided for each nozzle 244 of the inkjet head 242. Details of the drive circuits 110 will be explained in detail later with reference to Figures 6 to 8.

[0053] The image formed on the recording material P by the head unit 24 is read by the image reading unit 26, and the image data is sent to the control unit 40. When determining whether a nozzle 244 has a ejection defect, the control unit 40 identifies the nozzle 244 that is experiencing an ejection defect based on the image data sent from the image reading unit 26. The control unit 40 then performs shading correction processing on the head unit 24, for example, by increasing the amount of ink ejected from the nozzle 244 adjacent to the nozzle 244 that is experiencing an ejection defect.

[0054] [Configuration of the head drive unit] Next, the configuration of the head drive device provided in the inkjet recording device 1 will be explained with reference to Figure 6. Figure 6 is a circuit diagram showing an example of the configuration of the head drive device provided in the inkjet recording device 1.

[0055] As shown in Figure 6, the head drive device 100 includes a control circuit 101, a drive signal generation circuit 102, and a drive circuit 110. For example, the control circuit 101 is a controller configured using an FPGA (Field Programmable Gate Array) or the like, and operates based on instructions from the CPU 41. The control circuit 101 determines the waveform of the multidrop drive voltage based on head drive data generated from image data. The head drive data includes data such as the voltage during the ON period of the multidrop drive voltage waveform and the ON / OFF combinations of switches S1 to S4, which are compiled into a table and stored in the ROM 43 or storage unit 44, etc. The control circuit 101 then generates a control signal corresponding to the waveform of the multidrop drive voltage and outputs it to the drive signal generation circuit 102. The configuration or function of the control circuit 101 may be incorporated into the control unit 40, which includes the CPU 41.

[0056] The drive signal generation circuit 102 generates drive signals to be supplied to the series-connected switching elements 113 and 114 formed in the drive circuit 110, based on the control signal received from the control circuit 101. The drive signal generation circuit 102 is composed of an IC (Integrated Circuit), but like the control circuit 101, it can also be composed using an FPGA. The switching elements 113 and 114 are exclusively turned on or off based on the drive signals input to their respective gate terminals from the drive signal generation circuit 102. The drive signal generation circuit 102 may also be provided within the drive circuit 110.

[0057] The drive circuit 110 includes a power supply circuit 111, a capacitive load 112, a switching element 113, a switching element 114, and a boost circuit 120. The load 112 is a piezoelectric element (piezo element) of a nozzle actuator provided for each nozzle 244 of the inkjet head 242. In this embodiment, MOSFETs are used for the switching elements 113 and 114, but FETs or bipolar transistors may also be used. The switching element 113 is a P-channel MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and the switching element 114 is an N-channel MOSFET, but the channels may be reversed.

[0058] The power supply circuit 111 is a constant voltage source that outputs a power supply voltage Va (an example of a first power supply voltage). The output side of the power supply circuit 111 is connected to ground potential via a series connection of switching elements 113 and 114. In addition, one end of a load 112 is connected to the path between the source terminal of switching element 113 and the drain terminal of switching element 114, and the other end of the load 112 is connected to ground potential.

[0059] The boost circuit 120 comprises a power supply circuit 115, a diode Di, capacitors C1 and C2 (an example of a boost section), and switches S1 to S4 (an example of a switching section). Capacitors C1 and C2 are connected in parallel through switches S1 and S2. The number of capacitors is not limited to two, but may be three or more.

[0060] The output side of the power supply circuit 115 is connected to the path between the output side of the power supply circuit 111 and the drain terminal of the switching element 113 via diode Di and switch S4. One end of capacitor C1 is connected to the path between the cathode of diode Di and switch S4. The other end of capacitor C1 is connected via switch S1 to the path between the midpoint of the connection between the source terminal of switching element 113 and the drain terminal of switching element 114 and one end of load 112. One end of capacitor C2 is connected via switch S2 to the path between the cathode of diode Di and switch S4. The other end of capacitor C2 is connected to the path between the midpoint of the connection between the source terminal of switching element 113 and the drain terminal of switching element 114 and one end of load 112. One end of switch S3 is connected to the path between the other end of capacitor C1 and switch S1, and the other end of switch S3 is connected to the path between switch S2 and one end of capacitor C2.

[0061] The switching elements 113 and 114 are turned on or off by the drive signal output from the drive signal generation circuit 102, charging the load 112 with the power supply voltage output by the power supply circuits 111 and 115, or discharging the power supply voltage charged to the load 112. In this way, the drive voltage is applied to the load 112 using the power supply voltage Va of the power supply circuit 111 and the power supply voltage Vb of the power supply circuit 115. The power supply voltage Vb may be the same as the power supply voltage Va. For example, the power supply voltage Va may be used as the power supply voltage used for boosting in the boost circuit 120.

[0062] The switching operation of switches S1 to S4 is controlled by the control circuit 101. Capacitors C1 and C2 charge the power supply voltage Vb (an example of a second power supply voltage) output by the power supply circuit 115, thereby generating a voltage to be superimposed on the power supply voltage Va (an example of a first power supply voltage) output by the power supply circuit 111. Capacitors C1 and C2 are selectively switched by switches S1 to S4 (especially switches S1 and S2) connected to each capacitor as a switching unit. A boost circuit 120 equipped with capacitors C1 and C2 and switches S1 to S4, which superimposes the voltage obtained by charging the capacitors onto the drive voltage of the load 112 (in this case, the power supply voltage Va) to boost the drive voltage, is also called a bootstrap circuit.

[0063] Based on the image data (head drive data) recorded on the recording material, the control circuit 101 selects whether or not to superimpose the voltages generated by multiple capacitors C1 and C2 onto the first power supply voltage Va each time an ink droplet is ejected, and to what extent to superimpose those voltages. Then, in between the on periods of the drive voltage waveform, the control circuit 101 switches the multiple capacitors C1 and C2 to change the voltage superimposed on the first power supply voltage Va.

[0064] When switching element 113 is off and switching element 114 is on, closing switches S1 and S2 charges the parallel-connected capacitors C1 and C2 from the power supply circuit 115. Then, a potential difference equal to the power supply voltage Vb is generated across capacitors C1 and C2. Subsequently, by switching switches S1 to S4 connected to capacitors C1 and C2, and switching the connection of capacitors C1 and C2 in series, a voltage that is an integer multiple of the power supply voltage Vb can be superimposed on the power supply voltage Va when switching element 113 is turned on and switching element 114 is turned off. In the example in Figure 6, by changing the combination of opening and closing switches S1 to S4, a voltage from 0 to 2 times the power supply voltage Vb can be superimposed on the power supply voltage Va.

[0065] The multidrop drive voltage waveform has one or more on periods for ejecting ink droplets from the nozzle 244 for each dot where an ink droplet should be ejected. The control circuit 101 switches the voltage value for each on period of the multidrop drive voltage waveform by switching between multiple voltages generated by multiple capacitors C1 and C2 for each on period of the multidrop drive voltage waveform. In other words, by switching switches S1 to S4 before the on period of the multidrop drive voltage waveform, the voltages for the first, second, third, ... shots can be adjusted to different voltages.

[0066] As described above, the inkjet recording apparatus 1 according to this embodiment includes a head drive device 100 configured to eject ink droplets from the nozzles 244, which includes a drive circuit (drive circuit 110) that applies a drive voltage to a nozzle actuator (capacitive load 112) provided corresponding to the nozzles 244 of the inkjet head 242, and a control unit (control circuit 101) that controls the drive of the drive circuit 110. The above-described drive circuit includes a plurality of boost units (e.g., capacitors C1, C2) that can generate a voltage superimposed on a first power supply voltage (power supply voltage Va) using a second power supply voltage (power supply voltage Vb), and a plurality of switching units (e.g., switches S1 to S4) that can switch between the plurality of voltages generated by the plurality of boost units. The control unit is configured to control the operation of the plurality of switching units and selectively superimpose the plurality of voltages generated by the plurality of boost units onto the first power supply voltage to generate the above-described drive voltage.

[0067] The configuration of the drive circuit 110 applies to all or more drive circuits that apply a drive voltage to the nozzle actuator (load 112) and are provided on the same circuit board (for example, the circuit board that constitutes the head drive unit 241 (see Figure 5)).

[0068] [Boosting the drive voltage through charge charging and discharge in a boost circuit] Next, the boosting of the drive voltage by charging and discharging in the boost circuit 120 of the drive circuit 110 will be explained with reference to Figures 6 and 7. The example shown in Figures 7 and 8 is an example in which a voltage of 2Vb, which is twice the power supply voltage Vb, is superimposed on the power supply voltage Va using the boost circuit 120.

[0069] Figure 7 shows the state when the boost circuit 120 is charged in the drive circuit 110, and the equivalent circuit of the drive circuit 110. As shown in the upper part of Figure 7, the control circuit 101 closes switches S1 and S2 and opens switches S3 and S4, connecting capacitors C1 and C2 in parallel. Then, the control circuit 101 turns off switching element 113 and turns on switching element 114, supplying the power supply voltage Vb output from the power supply circuit 115 to capacitors C1 and C2, thereby charging capacitors C1 and C2.

[0070] If the voltage value of the power supply voltage Vb is "Vb", then, as shown in the equivalent circuit 110E1 in the lower part of Figure 7, the potential difference generated across the parallel connected capacitors C1 and C2 is "Vb".

[0071] Figure 8 shows the state when the charge charged in the boost circuit 120 is superimposed on the output of the drive circuit 110, and the equivalent circuit of the drive circuit 110. As shown in the upper part of Figure 8, the control circuit 101 opens switches S1 and S2 and closes switches S3 and S4 from the state shown in the upper part of Figure 7, switching capacitors C1 and C2 from parallel connection to series connection. Then, the control circuit 101 turns on switching element 113 and turns off switching element 114, discharging the charge charged in capacitors C1 and C2.

[0072] If the voltage value of the power supply voltage Va is "Va", then the potential difference between the series-connected capacitors C1 and C2 is "2Vb", as shown in the equivalent circuit 110E2 in the lower part of Figure 8. Therefore, the driving voltage applied to the load 112 is "Va + 2Vb".

[0073] Thus, in the boost circuit 120 of this embodiment, the multiple capacitors C1 and C2 are switched between parallel and series connections in accordance with the switching operation of the multiple switches S1 to S4. In addition, the multiple capacitors C1 and C2 are selectively switched between charging and discharging the second power supply voltage Vb in accordance with the switching operation of the multiple switches S1 to S4.

[0074] Figure 9 is a waveform diagram showing an example of the multidrop drive voltage according to this embodiment. As shown in Figure 9, in this embodiment, by switching switches S1 to S4 in the multidrop circuit, the voltage during the ON period of the multidrop drive voltage waveform can be changed within the range of "Va" to "Va + Vb * N" times. N is the number of capacitors connected in series that constitute the boost circuit 120. In this embodiment, the maximum number of capacitors connected in series is 2.

[0075] Figure 9 shows an example of a multidrop drive voltage waveform composed of three ON periods. In this example, the voltage during the first ink droplet ejection is "Va", the voltage during the second ejection is "Va + 2Vb", and the voltage during the third ejection is "Va + Vb". The dot diameters of ink droplets D1 to D3, ejected three times consecutively for a single dot, are smallest for ink droplet D1, largest for ink droplet D2, and intermediate for ink droplet D3.

[0076] The multidrop drive voltage waveform shown in Figure 9 is just one example. In the multidrop drive voltage waveform, the number of ON periods (number of ink droplet ejections) and the voltage during the ON period are determined by head drive data based on image data.

[0077] To obtain the voltage "Va + Vb" in the multidrop drive voltage waveform, for example, in the upper part of Figure 8, switch S3 is opened and only the voltage "Vb" charged to capacitor C1 is superimposed on the drive voltage Va. For example, in the upper part of Figure 8, by keeping at least switch S4 open, the power supply voltage "Va" is applied to the load 112. In the example described above, both capacitors C1 and C2 are charged, but it is also possible to configure the system to arbitrarily charge capacitors C1 and C2 according to the voltage superimposed on the power supply voltage Va (for example, 0, Vb, 2Vb). Alternatively, switches S1 to S4 may be switched between each on period of the multidrop drive voltage waveform to charge capacitors C1 and / or C2.

[0078] As described above, the head drive unit 100 of the inkjet recording apparatus 1 according to this embodiment generates a drive voltage for the nozzle actuator (load 112) by selectively superimposing multiple voltages onto a first power supply voltage (power supply voltage Va). For this reason, the head drive unit 100 uses multiple capacitors (for example, capacitors C1, C2) in the boost circuit 120, and the connection configuration of the multiple capacitors can be switched by switches S1 to S4 between ink droplet ejection in a multi-drop. In other words, the head drive unit 100 has multiple voltages that can be boosted in the boost circuit 120, and by selectively superimposing these voltages onto the first power supply voltage (power supply voltage Va), it is possible to switch between multiple voltages (for example, "Va", "Va+Vb", "Va+2Vb") generated by the boost within a multi-drop.

[0079] Therefore, the head drive device 100 with the above configuration can change the dot diameter of each ink droplet ejected during multi-drop printing by changing the voltage values ​​of multiple on-periods in the multi-drop drive voltage waveform, thereby changing the dot diameter for each individual dot. Thus, the head drive device 100 can increase the degree of freedom in controlling the dot diameter for each individual dot during multi-drop printing.

[0080] Furthermore, the inkjet recording apparatus 1 equipped with the head drive device 100 described above can achieve a multi-drop drive voltage waveform while varying the voltage, while keeping circuit costs and mounting area low.

[0081] [Differentiation] It should be noted that the present invention is not limited to the embodiment described above, and various other applications and modifications are possible as long as they do not depart from the gist of the present invention as described in the claims. For example, the embodiment described above describes the configuration of an inkjet recording device (head drive device) in detail and specifically in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all the components described. Furthermore, it is possible to add, replace, or delete other components in some parts of the configuration of this embodiment. [Explanation of symbols]

[0082] 1…Inkjet recording device, 40…Control unit, 100…Head drive device, 101…Control circuit, 102…Drive signal generation circuit, 110…Drive circuit, 110E1,110E2…Equivalent circuit, 111…Power supply circuit, 112…Load, 113,114…Switching element, 115…Power supply circuit, 120…Boost circuit, C1,C2…Capacitor, Di…Diode, S1~S4…Switch, Va,Vb…Power supply voltage

Claims

1. A head drive device for an inkjet recording device that ejects ink droplets from a nozzle, comprising a drive circuit that applies a drive voltage to a nozzle actuator provided corresponding to the nozzle of an inkjet head, and a control unit that controls the drive of the drive circuit, The drive circuit includes a plurality of boost units that can generate a voltage superimposed on the first power supply voltage using a second power supply voltage, It comprises multiple switching units that can switch between multiple voltages generated by multiple voltage boosting units, The control unit controls the operation of the multiple switching units and generates the drive voltage by selectively superimposing the multiple voltages generated by the multiple boost units onto the first power supply voltage. The waveform of the drive voltage has one or more on periods for ejecting an ink droplet from the nozzle for a single dot from which the ink droplet is to be ejected. Head drive mechanism.

2. The control unit switches the voltage value of the drive voltage for each on-period by switching between multiple voltages generated by multiple boost units for each on-period of the drive voltage waveform. The head drive device according to claim 1.

3. The multiple boost units are multiple capacitors that generate the voltage to be superimposed on the first power supply voltage by charging the second power supply voltage. The multiple capacitors are selectively switched by a switch connected to each capacitor, which serves as the switching unit. The head drive device according to claim 2.

4. Multiple capacitors are configured to switch between parallel and series connections in accordance with the switching operation of multiple switches. The head drive device according to claim 3.

5. Multiple capacitors selectively switch between charging and discharging the second power supply voltage in accordance with the switching operation of multiple switches. The head drive device according to claim 4.

6. The multiple capacitors and the multiple switches constitute a boost circuit that can increase the first power supply voltage by a bootstrap circuit. The head drive device according to claim 5.

7. Based on the image data recorded on the recording material, the control unit selects whether or not to superimpose the voltage generated by the plurality of capacitors onto the first power supply voltage each time an ink droplet is ejected, and to what extent to superimpose the voltage, and between the on periods of the waveform of the drive voltage, The voltage superimposed on the first power supply voltage is changed by switching between the multiple capacitors. The head drive device according to claim 3.

8. The configuration of the aforementioned drive circuit applies to all or more drive circuits that apply a drive voltage to the nozzle actuator and are provided on the same circuit board. The head drive device according to any one of claims 1 to 6.

9. An inkjet recording apparatus having a drive circuit that applies a drive voltage to nozzle actuators provided corresponding to the nozzles of an inkjet head, and a control unit that controls the drive of the drive circuit, wherein ink droplets are ejected from the nozzles, The aforementioned drive circuit is Multiple boost units capable of generating a voltage superimposed on the first power supply voltage using a second power supply voltage, It comprises multiple switching units that can selectively switch between multiple voltages generated by multiple voltage boosting units, The control unit controls the operation of the multiple switching units and generates the drive voltage by selectively superimposing the multiple voltages generated by the multiple boost units onto the first power supply voltage. The waveform of the drive voltage has one or more on periods for ejecting an ink droplet from the nozzle for a single dot from which the ink droplet is to be ejected. Inkjet recording device.

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